fix: (vNet) class load issues for OSGi bundle.

Problem.
1. Inside incubator package, class loader can't search classes defined
   in the other bundles such as onos-core

Solution
1. Added a method to return bundle context, and obtain class loader.

Change-Id: If5ee4cb1a5b9ef5ab7d7e3bbc70408ea8257baea
diff --git a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkDeviceManager.java b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkDeviceManager.java
index c529061..0f47a29 100644
--- a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkDeviceManager.java
+++ b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkDeviceManager.java
@@ -61,7 +61,7 @@
      */
     public VirtualNetworkDeviceManager(VirtualNetworkService virtualNetworkManager,
                                        NetworkId networkId) {
-        super(virtualNetworkManager, networkId);
+        super(virtualNetworkManager, networkId, DeviceEvent.class);
         manager.addListener(virtualNetworkListener);
     }